logback中设置maxHistory属性无效？ 配置报错 

logback指定maxHistory，按照文档中说明测试，发现过期的日志归档文件并不能被删除：

The optional maxHistory property controls the maximum number of archive files to keep, deleting older files. For example, if you specify monthly rollover, and set maxHistory to 6, then 6 months worth of archives files will be kept with files older than 6 months deleted. Note as old archived log files are removed, any folders which were created for the purpose of log file archiving will be removed as appropriate.

<configuration>
  <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <file>logFile.log</file>
    <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
      <!-- daily rollover -->
      <fileNamePattern>logFile.%d{yyyy-MM-dd}.log</fileNamePattern>

      <!-- keep 30 days' worth of history -->
      <maxHistory>30</maxHistory>
    </rollingPolicy>

    <encoder>
      <pattern>%-4relative [%thread] %-5level %logger{35} - %msg%n</pattern>
    </encoder>
  </appender> 

  <root level="DEBUG">
    <appender-ref ref="FILE" />
  </root>
</configuration>